An alien race from Planet Vegeta, that are identical to humans in almost every way, except they have a tail, that if they look at a full moon with a tail, they transform into King Kong sized WereMonkeys, or Oozaru's, which can fire energy blasts from thier mouth usually, and rarely from other various parts of their body. This form lasts until the full moon sets, the saiyan is killed, or the saiyan loses his tail via sword, blast, or wish granted by the dragons Shenron or Parunga. Saiyans without the tail, when their power level is at almost 1 million, will mutate into a tailess super saiyan, i believe to be a hybrid form. This form has bulked up muscles and yellow hair, as well as a golden aura surrounding the saiyan. There are 3 stages or transformations of super saiyans, first is a "Super Saiyan". Second is an "Ascended Super Saiyan" or simply, a "Super Saiyan 2". Third is known as a "Double Ascended Super Saiyan" by Krillin, or more popularly by Goku as "Super Saiyan 3". Now the fun begins..There is a fourth form, in terms of power level and when this form was seen first. This fourth form is what I and some others consider the true form of a Super Saiyan. Dubbed simply, "Super Saiyan 4", this form is reached when a saiyan capable of going Super Saiyan, regains his tail, looks at a full moon, or something that produces the like or greater amount of Brute waves. The tailed saiyan then transforms into a "golden oozaru". When the saiyan starts to regain consciousness and control over that form, he transforms into a Super Saiyan 4. SS4's have long mid back length black hair, black eyebrows, red outlining their eyes, yellow eyes, red fur covering thier body and tail, and an increased amount of attitude and hatred..which i believe is what would make this the true form of Super Saiyan, because Goku or Kakarott was always playful, even as SS, SS2, and SS3. But when he undergoes SS4, all things jokingly were put aside, and only the desire to get the job done, quick and easy, was there. this idea tho is not a fact as we saw that when SS4 Goku and Vegeta fused to become SS4 Gogeta, Gogeta was an Arrogant fool who wasted his 30 minutes toying with Omega Shenron instead of Destroying him.

An alien race of warriors from the planet Vegeta. Humanoid with a tail. For thousands of years they traveled the universe conquering planets. A Saiyans body had the ability to obsorb ambient energy and channel & condense it into energy blast either beam or ball form. When they get injured and recovery their bodies heal stronger so every fight they increase their overall power level exponentially.

They are born with natural fighting skills:
Super speed - so fast an untrained eye cannot see them move
Flight by the power of their mind - simple ESP onto their own body to sustain flight
Extremely durable body
Quick healing

Can sense other life forms/power levels
Extreme vision, hearing and strength

At sight of full moon will transform into a 200 foot tall ape with
unstopable power - planet killers
Only way to stop is to destroy moon or cut off the tail

Let me put it like this...One Saiyan child is strong enough to take over and exterminate a planet the size of Earth.